Hydraulic pressure transformers are used to transform an input flow of hydraulic fluid at a first flow rate and pressure to an output flow of hydraulic fluid at a second flow rate and pressure. The output flow rate and pressure are variable to provide a variable output flow to a specific application, such as a hydrostatic transmission.
Conventional hydraulic pressure transformers may include a housing with a rotatable barrel and a movable port plate disposed therein. The port plate includes three arcuate slots which selectively interconnect a plurality of ports in the housing with a plurality of cylinders in the barrel upon rotation of the barrel during use. The relative position between the slots in the port plate and the ports in the housing define the output pressure from the hydraulic pressure transformer.
It is also known to provide a hydraulic pressure transformer with a port block instead of a port plate between the housing and barrel. The port block includes a spherical surface on each end thereof which abuts a complimentary spherical surface on the housing and barrel, respectively. The spherical surfaces at each end of the port block allow slight tipping or tilting between the housing, port block and barrel, while at the same time maintaining a substantially sealed relationship therebetween. Although effective to provide a substantially sealed contact between the abutting surfaces, the spherical surfaces at each end of the port block are relatively expensive to manufacture.
A port block as described above is typically rotatably carried within the housing by a pair of large diameter roller bearings which are seated within the housing and radially surround a port block. Both the housing and the port block are usually formed with stepped annular surfaces which are used to properly seat the roller bearing assemblies relative to each of the housing and the port block. The roller bearing assemblies, as well as the stepped annular shoulders which are formed to receive the bearing assemblies, increase the manufacturing complexity and cost of the hydraulic pressure transformer. A port block as described can experience a significant tipping moment as the various ports are exposed to varying pressure. The large diameter rolling element bearings are required to carry the moments and prevent tipping of the port plate.
The present invention is directed to overcoming one or more of the problems as set forth above.